Yup, via the TypeError in line 1400 now.  (Note that the 'should not be callable without "new"' test case below hasn't changed.)  The ES6 spec seems to avoid using `instanceof` tests, which are based on the `constructor` property; instead they use the presence/absence of certain hidden slots which are added via `@@create`.  I guess this is more robust, since `constructor` can be changed by the user?  At any rate, our logic better matches the spec now.